[NFC][sanitizer] Add test for command line flag for enable-noundef-analysis.

[kda]

Summary

A simple unit test to demonstrate the flags working correctly.

[kda]

remove unused include.

[kda]

removed more unnecessary code.

[vitalybuka]

Isn't more appropriate title "simplify test" something?
It looks like you removed unneeded code, but the test mostly the same.

compiler-rt/test/msan/noundef_analysis.cpp

+// RUN: %clangxx_msan %s -o %t && %run %t >%t.out 2>&1
+// RUN: FileCheck %s --check-prefix=MISSED --allow-empty < %t.out
+// RUN: %clangxx_msan %s -Xclang -enable-noundef-analysis -mllvm -msan-eager-checks=1 -o %t && not %run %t >%t.out 2>&1
+// RUN: FileCheck %s < %t.out
+
+struct SimpleStruct {
+  int md1;
+};
+
+static int sink;
+
+static void examineValue(int x) { sink = x; }
+
+int main(int argc, char *argv[]) {
+  auto ss = new SimpleStruct;
+  examineValue(ss->md1);
+
+  return 0;
+}
+
+// CHECK: WARNING: MemorySanitizer: use-of-uninitialized-value
+// MISSED-NOT: use-of-uninitialized-value